Magnetic recording medium having a specified plasma polymerized hydrogen containing carbon film and lubricant

ABSTRACT

A magnetic recording medium possessing excellent electromagnetic characteristics, corrosion resistance, durability, abrasion resistance and lubricity, has an undercoat layer, a ferromagnetic metal layer, a protective layer and a lubricating layer formed in this order on a non-magnetic substrate, or has an undercoat layer, a ferromagnetic metal layer, an intercepting layer, a protective layer and a lubricating layer formed in this order on a non-magnetic substrate, wherein the protective layer is a plasma-polymerized hydrogen-containing carbon film having a refractive index of 1.90 or more and a contact angle of less than 80 degrees, the film thickness of the protective layer or the total film thickness of the protective layer and the intercepting layer is 30 to 150 Å, the undercoat layer, as well as the intercepting layer, is a film formed of silicon oxide represented by SiOx (x=1.8-1.95), and the lubricating layer is formed of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds; and a method for producing the recording medium.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No. 08/350,070, filed on Nov. 29, 1994 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording medium and a method for producing the same, and more particularly to a magnetic recording medium in which a ferromagnetic metal layer serves as a magnetic layer, the ferromagnetic metal layer having improved corrosion resistance, durability, abrasion resistance and lubricity, and a method for its production.

2. Background Art

Magnetic recording media in which ferromagnetic metal layers serve as magnetic layers have excellent characteristics, such as high saturation magnetic flux density and coercive force.

Previously, various magnetic recording media and methods for their production have been proposed to improve the corrosion resistance, durability, abrasion resistance and lubricity of the magnetic recording media in which the ferromagnetic metal layers serve as the magnetic layers.

For example, Japanese Patent Unexamined Publication No. 4-341918 discloses a magnetic recording medium in which a ferromagnetic metal thin film serves as a magnetic layer, the magnetic recording medium comprising a non-magnetic resin substrate, an undercoat layer, a ferromagnetic metal film and a topcoat layer, the undercoat layer and the topcoat layer each containing C and H, and being plasma-polymerized films having a refractive index of 1.8 or more. Japanese Patent Unexamined Publication No. 5-20663 discloses a magnetic recording medium in which the undercoat layer is a plasma-polymerized film containing Si or Si and 0, and the topcoat layer is a plasma-polymerized film containing C and H. Japanese Patent Examined Publication No. 5-33456 discloses a magnetic recording medium comprising a substrate, a magnetic layer formed on the substrate and a protective layer formed on the magnetic layer, the protective layer comprising a hard carbon layer and a fluorine-containing lubricating oil layer. Japanese Patent Unexamined Publication No. 57-135443 discloses a magnetic recording medium in which a vapor stream of a magnetic substance is obliquely incident on a surface of a substrate to deposit a magnetic thin film, and immediately thereafter an organic substance is plasma polymerized on the deposited magnetic film to provide an overcoat thin-film layer. Japanese Patent Unexamined Publication No. 57-164432 discloses a magnetic recording medium in which an organic polymer layer is formed on an oblique deposition type metal magnetic layer and a higher fatty acid or ester layer is formed thereon, the organic polymer layer and the higher fatty acid or ester layer each being formed by vacuum deposition, ion plating, sputtering or plasma polymerization. Japanese Patent Examined Publication No. 3-53691 discloses a magnetic recording medium in which a surface of a magnetic layer is coated with a plasma-polymerized thin film having siloxane bonds and a thickness of 5 to 1000 Å.

However, for the prior-an magnetic recording media described in Japanese Patent Unexamined Publication Nos. 4-341918 and 5-20663, the protective layers have insufficient adhesive property and corrosion resistance. Further, the magnetic recording medium described in Japanese Patent Examined Publication No. 5-33456 has the disadvantage of rusting because of lack of an undercoat layer. The magnetic recording medium described in Japanese Patent Unexamined Publication No. 57-135443 in which the organic substance is plasma polymerized on the magnetic layer, and the magnetic recording medium described in Japanese Patent Unexamined Publication No. 57-164432 in which the higher fatty acid or ester is plasma polymerized on the magnetic layer are also not sufficient in corrosion resistance, lubricity and abrasion resistance. Furthermore, the magnetic recording medium described in Japanese Patent Examined Publication No. 3-53691 (Japanese Patent No. 1687307), in which the magnetic layer is coated with the plasma-polymerized film having siloxane bonds, has no undercoat layer, resulting in formation of rust, and is also poor in abrasion resistance.

Accordingly, a magnetic recording medium having a combination of corrosion resistance, abrasion resistance, friction resistance, durability and lubricity is desirable.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problem, the present inventors have conducted intensive investigations, and as a result have discovered that the problems can be solved (1) when a magnetic recording medium structurally comprises an SiOx film, a magnetic layer, a protective layer of a diamond like carbon (DLC) film, and further a lubricating layer, all formed on a substrate, said DLC film forming the protective layer being a plasma-polymerized hydrogen-containing carbon film having a specified refractive index and contact angle and formed by applying a negative bias to a base to adjust the frequency (audio frequency, or AF) on the electrode side to a specified value, said lubricating layer being formed of a specified fluorine compound, and (2) when a magnetic recording medium structurally comprises an SiOx film, a magnetic layer, an SiOx film, a protective layer (DLC film) and further a lubricating layer, all formed on a substrate, said DLC film forming the protective layer being a plasma-polymerized hydrogen-containing carbon film having a specified refractive index and contact angle and formed by applying a negative bias to a base to adjust the frequency (AF) on the electrode side to a specified value, said lubricating layer being formed of a specified fluorine compound, thus completing the present invention.

The present invention provides: (1) a magnetic recording medium comprising an undercoat layer, a ferromagnetic metal layer, a protective layer and a lubricating layer, all formed on a non-magnetic substrate in this order, wherein said protective layer is a plasma-polymerized hydrogen-containing carbon film (DLC film) having a refractive index of 1.90 or more, a film thickness of 30 to 150 Å and a contact angle of less than 80 degrees, said undercoat layer is a film formed of silicon oxide represented by SiOx (x=1.8-1.95), and said lubricating layer is formed of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds; (2) a magnetic recording medium comprising an undercoat layer, a ferromagnetic metal layer, an intercepting layer, a protective layer and a lubricating layer formed on a non-magnetic substrate in this order, wherein said protective layer is a plasma-polymerized hydrogen-containing carbon film (DLC film) having a refractive index of 1.90 or more and a contact angle of less than 80 degrees, said undercoat layer and said intercepting layer are films formed of silicon oxide represented by SiOx (x=1.8-1.95), the total film thickness of said protective layer and said intercepting layer is 30 to 150 Å and said lubricating layer is formed of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds; (3) the magnetic recording medium described in (1) or (2) above, wherein said ferromagnetic metal layer is formed by vapor deposition; (4) a method for producing the magnetic recording medium described in (1) above which comprises forming an undercoat layer of silicon oxide represented by SiOx (x=1.8-1.95) on a non-magnetic substrate, forming a ferromagnetic metal layer thereon in a vapor phase, then plasma polymerizing a hydrocarbon gas and hydrogen at a frequency of 50 kHz to 450 kHz while applying a negative bias to a base side to form a protective layer of a hydrogen-containing carbon film having a refractive index of 1.90 or more, a contact angle of less than 80 degrees and a film thickness of 30 to 150 Å and finally forming a lubricating layer of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds; (5) a method for producing the magnetic recording medium described in (2) above which comprises forming an undercoat layer of silicon oxide represented by SiOx (x=1.8-1.95) on a non-magnetic substrate, forming a ferromagnetic metal layer thereon in a vapor phase, forming an intercepting layer of a film formed of silicon oxide represented by SiOx (x=1.8-1.95) by plasma polymerization, then plasma polymerizing a hydrocarbon gas and hydrogen at a frequency of 50 kHz to 450 kHz while applying a negative bias to a base side to form a protective layer of a hydrogen-containing carbon film having a refractive index of 1.90 or more and a contact angle of less than 80 degrees, adjusting the total film thickness of the protective layer and the intercepting layer to 30 to 150 Å, and finally forming a lubricating layer of a compound selected from the group consisting of polar perfluoro-polyethers, non-polar perfluoropolyethers, perfluoro-carboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds; (6) the method described in (4) or (5) above, wherein the negative bias is a pulse bias, the pulse duty factor (ON/OFF ratio) is 0.3 to 3, and the frequency is 10 Hz to 500 Hz; and (7) the method described in (4) or (5) above, wherein the formation of the ferromagnetic metal layer in the vapor phase is by vapor deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view showing an apparatus for producing a DLC film used in the present invention. In the figure, the reference numeral 1 designates electrodes, the reference numeral 2 designates a rotating drum, the reference numerals 3 and 4 designate guide rolls, respectively, the reference numeral 5 designates a tape take-up roll, the reference numeral 6 designates a tape unwinding roll, and the reference numeral 7 designates a power supply for a DC bias.

FIG. 2 is a schematic, to an enlarged scale, of a water droplet on a surface, showing how the contact angle (θ) is determined.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, the plasma-polymerized hydrogen-containing carbon film having a refractive index of 1.90 or more and a contact angle of less than 80 degrees is used as the protective layer, said film being formed by plasma polymerization by applying an audio frequency (AF) of 50 kHz to 450 kHz to the electrode side and a negative bias to the base side.

The plasma polymerization can be achieved by any known methods, for example the method described in Japanese Patent Examined Publication No. 3-53691. A vacuum chamber in which electrodes are arranged is evacuated to 10⁻⁶ Torr, and specific amounts of a raw material gas and hydrogen gas are introduced thereinto by use of a mass flow controller. After maintenance at a specified pressure, an electrical discharge is generated with an AF power supply, and the speed of a running system of a tape is controlled to give a required film thickness. In preparing the DLC film, a DC bias is applied to an electrode on the base side. Then, the vacuum is broken, and the resulting sample on which a polymerized film is formed is taken out.

As the raw materials for the plasma-polymerized hydrogen-containing carbon film forming the protective layer, various gases containing carbon and hydrogen can be used. Usually, one or more of methane, ethane, propane, butane, pentane, ethylene, propylene, butene, butadiene, acetylene, methylacetylene, and other saturated and unsaturated hydrocarbons which are gaseous at ordinary temperatures are used as carbon and hydrogen sources because of their good operability.

When the hydrocarbon gas is plasma polymerized, an audio frequency of 50 kHz to 450 kHz is applied. An audio frequency of less than 50 kHz approaches direct current (DC) in properties. Hence, discharges become unstable as the films are overlapped on the periphery according to long-term operation, which causes abnormal film quality. In addition, great damage due to ions causes damaged properties of the tape. Further, an audio frequency exceeding 450 kHz causes sluggish movement of ions, resulting in soft film quality. The resulting film is therefore poor in durability.

As to the negative bias, a negative potential is applied by DC. A pulse bias is preferably used. As the bias, there also is radio frequency (RF) bias. However, although the RF bias produces a negative potential, the negative potential is partially reversed to a positive potential. Accordingly, a completely negative potential is not necessarily obtained. Experiments show that this case was little different in properties from the case when no bias was applied.

Even when the DC bias is merely applied, the effect is manifested. However, when the DC bias is further pulsed, the sufficient bias effect is obtained even through an insulator for further improvement.

The pulse duty factor (ON/OFF ratio) is preferably 0.3 to 3. A pulse duty factor of less than 0.3 causes unstable discharges, and a pulse duty factor exceeding 3 results in no difference from the case when the DC is applied as a continuous wave (CW). The pulse duty factor is further desirably about 0.8 to 1.5.

Further, the frequency is preferably 10 Hz to 500 Hz. If the frequency is less than 10 Hz, the bias applying effect is not obtained. If the frequency exceeds 500 Hz, the film is not hardened because of its high-frequency behavior.

The refractive index of the plasma-polymerized hydrogen-containing carbon film in the present invention is 1.9 or more. A refractive index of less than 1.9 results in a significant decrease in durability and also deterioration of keeping characteristics. This is because the film hardness is lowered and a decrease in film density allows water to easily pass through the film. The reason for this is that the increased content of hydrogen in the film makes it impossible to form a cross-linked structure.

The plasma-polymerized hydrogen-containing carbon film of the magnetic recording medium of (1) mentioned above of the present invention has a film thickness of 30 to 150 Å. If the film thickness is less than 30 Å, the effect is not manifested. If the film thickness exceeds 150 Å, the electromagnetic characteristics of the deposited tape itself is affected because of the great spacing loss. Further, the contact angle thereof is less than 80 degrees. If the contact angle shows a value of 80 degrees or more, the still characteristics (durability) is not improved because of insufficient production of C═C on a surface of the film. With respect to such a film having a refractive index of 1.90 or more and a contact angle of less than 80 degrees, the methyl-methylene absorption appearing at 2,900 cm⁻¹ in Fourier transform infrared (FTIR) spectroscopy is little observed.

The total film thickness of the plasma-polymerized hydrogen-containing carbon film and the intercepting layer of the magnetic recording medium of (2) mentioned above of the present invention is 30 to 150 Å. If the film thickness is less than 30 Å, the effect is not manifested. If the film thickness exceeds 150 Å, the electromagnetic characteristics of the deposited tape itself are affected because of the great spacing loss. Further, the contact angle thereof is less than 80 degrees. If the contact angle shows a value of 80 degrees or more, the still characteristics are not improved because of insufficient production of C═C on a surface of the film. With respect to such a film having a refractive index of 1.90 or more and a contact angle of less than 80 degrees, the methyl-methylene absorption appearing at 2,900 cm⁻¹ in FTIR is little observed.

The undercoat layer of the magnetic recording medium of (1) mentioned above is a film formed of silicon oxide represented by SiOx (X=1.8-1.95). In silicon oxide wherein x is less than 1.8, carbon is left in the film, so that the density is not increased. Hence, the water-intercepting property is not manifested. Silicon oxide wherein x exceeds 1.95 is also insufficient in water-intercepting property to function properly as a water-intercepting layer. By the use of electron spectroscopy for chemical analysis (ESCA), it has been determined that the film formed of silicon oxide wherein x is less than 1.8 contains 15 atomic % of unreacted carbon atoms based on all atoms, whereas the film formed of silicon oxide wherein x is 1.8 or more contains less than 1 atomic % of unreacted carbon atoms because the reaction proceeds sufficiently. It becomes clear that the carbon content has a significant effect on water-intercepting property.

The undercoat layer and the intercepting layer of the magnetic recording medium of (2) mentioned above are films formed of silicon oxide represented by SiOx (x=1.8-1.95). In silicon oxide wherein x is less than 1.8, carbon is left in the film, so that the density is not increased. Hence, the water-intercepting property is not manifested. Silicon oxide wherein x exceeds 1.95 is also insufficient in water-intercepting property to function properly as a water-intercepting layer. By the use of electron spectroscopy for chemical analysis (ESCA), it has been determined that the film formed of silicon oxide wherein x is less than 1.8 contains 15 atomic % of unreacted carbon atoms based on all atoms, whereas the film formed of silicon oxide wherein x is 1.8 or more contains less than 1 atomic % of unreacted carbon atoms because the reaction proceeds sufficiently. It becomes clear that the carbon content has a significant effect on water-intercepting property.

The film formed of silicon oxide represented by SiOx (x=1.8-1.95) is prepared by evacuating a vacuum chamber to 10⁻⁶ Torr, then introducing specific amounts of a raw material gas and oxygen gas thereinto by use of a mass flow controller, and generating plasma with an AF power supply. In the case of the DLC film, a DC bias is applied. For the SiOx film, however, such bias is not particularly necessary though it may be applied, with the proviso that the introducing flow ratio of the raw material silane series gas to the oxygen gas (Si/O₂) is required to be 1/3. If the oxygen flow rate is less than this ratio, the film formed of silicon oxide wherein x is 1.8 or more can not be obtained.

The silane series gases used as the raw materials include silane, trimethylsilane, tetramethylsilane, trimethoxysilane, tetramethoxysilane and tetraethoxysilane. From the viewpoint of handling, the materials which are liquid under the standard conditions of 0° C. and 1 atm. are easily handled. As to the boiling point, the materials having a boiling point of about 100° C. are easily handled. The liquid raw materials may be supplied through a mass flow controller by use of a commercial liquid feeder.

The lubricating layer is formed by applying a solution of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds in a solvent. Usually, there is no particular restriction on coating methods, as long as they are methods used for coating of the magnetic recording media, such as gravure coating, reverse coating and die nozzle coating. The concentration of the lubricant based on the solvent is adjusted to within 1 to 0.1% by weight.

Examples of the polar perfluoropolyethers include Crylocks (E. I. Du Pont), Z-DOL, AM2001 (Monte Dison) and SA1, SY3 (Daikin Kogyo Co.). Examples of the non-polar perfluoro-polyethers include S20 (Daikin Kogyo Co.), examples of the perfluorocarboxylic acids include n-C_(m) F_(l) COOH (m=7-10,l=14-21), examples of the perfluoroalkylates include FA108 (Kyoeisha Yushikagaku Kogyo Co.), and examples of the perfluoro-acrylate compounds include n-C_(m) F_(l) COOC_(p) F_(q) (p=7-10,q=14-21, m and l are as defined above).

As the solvents, flon solvents such as L-90, and tributylamine solvents such as EFL-150 (Daikin Kogyo Co.) are used.

Compounds other than these lubricants, for example, saturated carboxylic acids such as stearic acid and myristic acid and silicone oil, do not give the effect. Fluorine lubricants having low surface energy are preferred for the magnetic metal layers.

As the non-magnetic substrates, various usual films are used, as long as they resist heat on vapor deposition of the ferromagnetic metal thin films. Examples of such films include films of polyesters, polyimides, aramides, polysulfones, polyether ether ketone (PEEK). Films of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are used.

Metals such as Fe, Co and Ni and various alloys thereof are used in the ferromagnetic metal layers. Co or alloys mainly composed of Co are preferred. The alloys mainly composed of Co include Co--Ni, Co--Fe, Co--Cr, Co--Ni--Cr, Co--Pt--Cr, Co--Cu, Co--Sm and Co--P. The Co--Ni alloys are preferably used, and alloys containing about 80% or more of Co and less than 20% of Ni in molar ratio are particularly preferred. These ferromagnetic metal thin layers are formed by metal thin layer forming methods such as vacuum deposition, ion plating and sputtering. Deposition is preferably used, and oblique deposition is particularly preferred. Oxidative gases such as oxygen may be introduced during formation of the films. The thickness of the magnetic layer is 500 to 3000 Å, and preferably 1500 to 2000 Å.

In the magnetic recording medium having the ferromagnetic metal layer serving as the magnetic layer, (i) the undercoat layer on the ferromagnetic metal layer is the film formed of silicon oxide represented by SiOx (x=1.8-1.95), and the protective layer is the plasma-polymerized hydrogen-containing carbon film having a refractive index of 1.90 or more, a film thickness of 30 to 150 Å and a contact angle of less than 80 degrees, which is prepared by plasma polymerization while applying an audio frequency of 50 kHz to 450 kHz to the electrode side and a negative bias to the base side; or (ii) the undercoat layer and the intercepting layer on the ferromagnetic metal layer are the films formed of silicon oxide represented by SiOx (x=1.8-1.95), the protective layer is the plasma-polymerized hydrogen-containing carbon film having a refractive index of 1.90 or more and a contact angle of less than 80 degrees, which is prepared by plasma polymerization while applying an audio frequency of 50 kHz to 450 kHz to the electrode side and a negative bias to the base side, and the total thickness of the protective layer and the intercepting layer is 30 to 150 Å; and the lubricating layer is formed of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds; whereby the excellent characteristics of the magnetic recording medium having the ferromagnetic metal layer serving as the magnetic layer are maintained, and the corrosion resistance, durability, abrasion resistance and lubricity thereof are improved.

As used herein, the term "contact angle" has the same meaning as commonly used and understood in the art. Definitions can be found, for example, in McGraw-Hill Encyclopedia of Science & Technology, 7th. edition, McGraw-Hill, Inc., New York, 1992, Van Nostrand's Scientific Encyclopedia, 8th. edition, Van Nostrand Reinhold, New York, 1995, and the Dictionary of Physics, edited by John Daintith, Barnes & Noble Books, 1981.

In the wetting or nonwetting of solids by liquids, the usual criterion is the contact angle between the solid and the liquid, as measured through the liquid. When a liquid wets the surface well, i.e., good adhesion, the contact angle is an acute angle, between 0 to 90°, and when the liquid does not wet the surface well, i.e., low adhesion, the contact angle is an obtuse angle, greater than 90°. Since an object of the present invention is to provide a magnetic recording medium having improved corrosion resistance by preventing, with a protective layer, the penetration to the magnetic layer of corrosion-causing liquid, the "wetting" of the surface of the protective layer as indicated by the contact angle being less than 80°, is a useful gauge of the adhesiveness of the protective layer as formed for the overlying lubricating layer which is applied thereto, and the adhesiveness of the protective layer to the underlying magnetic layer, or to the intermediate layer in the alternate embodiment. Thus, with a contact angle less than 80°, the protective layer as formed adheres well to the underlying magnetic film layer or intermediate layer, and provides good adhesiveness for the overlying lubricating layer.

The value of the contact angle depends on the various conditions for forming the protective layer on the magnetic recording tape by plasma polymerization of hydrocarbon gas and hydrogen gas. These conditions include plasma frequency, the use of pulse bias or continuous wave (CW), pulse duty factor and the voltage of the minus bias. In order to obtain a smaller value of contact angle (less than 80°), the following conditions are selected: (1) lower plasma frequency; (2) employment of a pulse bias rather than CW; (3) pulse duty factor between 0.3 and 3; and (4) a larger minus bias value number.

The apparatus used for measuring the contact angle is a contact angle meter, available commercially from Kyowa Kaimen Kagaku Co., Japan. In use, a sample of magnetic recording tape is place on a vertically-adjustable sample stand, with the protective layer of the tape facing upwardly. Ion-exchanged water is dropped from an injector of the apparatus to make a droplet approximately 2 mm in diameter. The water droplet is formed on the tape sample by raising and lowering the sample stand as necessary.

FIG. 2 shows how the contact angle is determined. A water droplet D has been formed on a solid surface S, such as the surface of a protective layer of DLC film. The contact angle theta (θ) is measured with respect to a tangent line at the interface between the water droplet, the surface of the solid, and the surrounding atmosphere, and is determined as follows:

θ=2(θ₁)

θ=-2 tan¹ (h/b)

where b=1/2 the base B of the water droplet

h=height of the water droplet

The pulse duty factor is the ratio of the time the pulse electric power is applied (ON) to the time the power is not applied (OFF). Generally, when pulse electric power is used, power is applied at a constant interval.

A discharge gives various species. Since a discharge by pulse is intermittent, plasma growth is limited. As a result, plasma is a group of species which have small distribution, is formed under pulse conditions. A film which is made from such plasma is homogeneous. Control of the pulse duty factor between 0.3 and 3 makes the contact angle less than 80°.

The film thickness and refractive index are measured by ellipsometry, a common technique for determining the properties of a material from the characteristics of polarized light reflected from its surface. When the electromagnetic waves comprising the light are reflected from the surface of the material, the amplitude of the reflected wave depends upon the properties of the material, the angle of incidence and the polarization of the wave. Further information on ellipsometry, and the procedures and apparatuses involved, can be found in most technical reference publications, such as McGraw-Hill Encyclopedia of Science & Technology and Van Nostrand's Scientific Encyclopedia, both cited above.

The composition of the SiOx film can be determined by electron spectroscopy for chemical analysis, or ESCA, also a known analytic technique. Electron spectroscopy is the study of the energy spectra of photoelectron or Auger electrons emitted from a substance upon bombardment by electromagnetic radiation, electrons, or ions, and is commonly used to investigate atomic, molecular or solid-state structure, and in chemical analysis. ESCA, also sometimes known as x-ray photoelectron spectroscopy, is a form of electron spectroscopy in which a sample is irradiated with a beam of monochromatic x-rays and the energies of the resulting photoelectrons are measured. Additional details on ESCA, and its use to determining chemical composition, can be found in most technical reference publications, such as the McGraw-Hill Encyclopedia of Science & Technology, cited above, Volume 6.

The present invention is described further with reference to the following examples. The characteristics of the magnetic recording tapes were measured as follows:

(1) Still Durability

A signal at 7 MHz was recorded under conditions of 40° C. and 20% relative humidity (RH), and the time required until its output reached -5 dB was measured.

(2) Corrosion Resistance

Each sample was kept under conditions of 60° C. and 90% RH for 1 week, and the reduction rate in saturation magnetic flux density was measured.

(3) Initial Friction

The friction coefficient at the first pass was measured with a commercially-available 180-degree pin friction tester.

(4) Durable Friction

The friction coefficient at the 500th pass was measured with a 180-degree pin friction tester.

(5) Surface Observation

The surface condition of each sample after 200 passes was observed under an optical microscope to examine the extent of surface scratching. No scratch is indicated by ◯, 1 to 5 scratches by Δ, and 6 scratches or more by X.

(6) Electromagnetic Characteristics

When the output at 7 MHz in Comparative Example 1 given below was taken as 0 dB, a difference in output between the sample in Comparative Example 1 and each sample of less than 2 dB is indicated by ◯, and a difference of 2 dB or more by X.

A. Magnetic Recording Media of (1)

EXAMPLES 1 TO 20 AND COMPARATIVE EXAMPLES 1 TO 29

The inside of a chamber was evacuated to 10⁻⁶ Torr, and then tetramethoxysilane as a raw material and oxygen were introduced thereinto at a ratio of 1:3, followed by adjustment of the pressure to 10⁻² Torr. Then, an audio frequency of 100 kHz was applied to an electrode to generate plasma discharges and to plasma polymerize SiOx having each of the various compositions shown in Tables 1-1 to 1-5, thereby forming an undercoat layer on a polyethylene terephthalate film substrate having a thickness of 7 μm. The x value in the SiOx film was changed by varying the ratio of oxygen introduced together with the silane series organic compound.

Subsequently, an alloy containing 80% by weight of Co and 20% by weight of Ni was deposited under an oxygen atmosphere to form a ferromagnetic metal layer (with a film thickness of 1,500 Å). A protective layer was formed thereon by plasma polymerization using methane as a hydrocarbon source by use of a DLC film producing apparatus such as shown in FIG. 1. Namely, the inside of a chamber was evacuated to 10⁻⁶ Torr, and then methane as a raw material and hydrogen were introduced thereinto at a ratio of 1:1, followed by adjustment of the pressure to 10⁻² Torr. Then, electromagnetic waves were applied to electrodes at high frequency to generate plasma discharges. At the same time, a DC bias was applied with the connections as shown in FIG. 1.

The protective layer was further coated by gravure coating with a solution prepared by dissolving each of the various lubricants shown in Tables 1-6 to 1-10 in a solvent, EFL-150 (Daikin Kogyo Co.), in a concentration of 0.3% by weight. The film thickness was about 40 Å. As the DC bias on the base side, one having a pulse generation mechanism was used.

S20 (Daikin Kogyo Co.) was used as a non-polar perfluoro-polyether (PFPE), KF-851 (Shinetsu Kagaku kogyo Co.) as silicone oil, SAl (Daikin Kogyo Co.) as a polar PFPE, n-C₁₀ F₂₀ COOH as a perfluorocarboxylic acid (PFA), phosphazene (Idemitsu Sekiyu Kagaku Co.) as a phosphazene, FA108 (Kyoeisha Yushikagaku Kogyo Co.) as a perfluoroacrylate, and n-C₁₀ F₂₀ COOC₁₀ F₂₀ as a perfluoroalkylate to form a lubricating layer.

The composition and the film thickness of the SiOx undercoat layers, the plasma frequency and the bias on film formation of the plasma-polymerized hydrogen-containing carbon film protective layers, and the film thickness, the refractive index and the contact angle of the resulting protective layers are shown in Tables 1-1 to 1-5. When the pulse bias is used, the pulse is 50 Hz. Further, for the resulting magnetic recording tapes, the materials of the lubricating layers, the still time, the corrosion resistance, the initial friction, the durable friction, the results of surface observation and the electromagnetic characteristics are shown in Tables 1-6 to 1-10.

The film thickness and the refractive index were measured by ellipsometry. The composition of SiOx was measured by ESCA. The contact angle was measured by a droplet dropping system using a contact angle meter (Kyowa Kaimen Kagaku Co.). For comparison, protective layers were formed using RF (radio frequency: 13.56 MHz) and 1 MHz.

                                      TABLE 1                                      __________________________________________________________________________     Protective Film (DLC Film)      Undercoat layer (SiOx)                               Plasma      Film          Film                                                 Frequency   Thickness                                                                           Refractive                                                                          Contact                                                                            Thickness                                                                            Value                                          (kHz)                                                                               Bias                                                                              Bias V                                                                             (Å)                                                                             Index                                                                               Angle                                                                              (Å)                                                                              of x                                     __________________________________________________________________________     Example 1                                                                            400  CW -200                                                                               100  1.95 77  200   1.9                                      Example 2                                                                            200  CW -200                                                                               100  1.97 77  200   1.9                                      Example 3                                                                            100  CW -200                                                                               100  1.98 76  200   1.9                                      Example 4                                                                             50  CW -200                                                                               100  2.0  75  200   1.9                                      Example 5                                                                            400  pulse                                                                             -200                                                                               100  1.97 75  200   1.9                                      Example 6                                                                            200  pulse                                                                             -200                                                                               100  1.98 75  200   1.9                                      Example 7                                                                            100  Pulse                                                                             -200                                                                               100  2.0  74  200   1.9                                      Example 8                                                                             50  pulse                                                                             -200                                                                               100  2.1  73  200   1.9                                      Example 9                                                                            400  CW -200                                                                                30  1.95 77  200   1.9                                      Example 10                                                                           400  CW -200                                                                                50  1.95 77  200   1.9                                      Example 11                                                                           400  CW -200                                                                               150  1.95 77  200   1.9                                      Example 12                                                                           400  CW -200                                                                               100  1.95 77  300   1.9                                      Example 13                                                                           400  CW -200                                                                               100  1.95 77  200   1.8                                      Example 14                                                                           400  CW -200                                                                               100  1.95 77  200   1.95                                     Example 15                                                                           400  CW -200                                                                               100  1.95 77  200   1.9                                      Exdmple 16                                                                           400  CW -200                                                                               100  1.95 77  200   1.9                                      Example 17                                                                           400  CW -200                                                                               100  1.95 77  200   1.9                                      Example 18                                                                           400  pulse                                                                             -200                                                                               100  1.97 75  200   1.9                                      Example 19                                                                           400  pulse                                                                             -200                                                                               100  1.97 75  200   1.9                                      Example 20                                                                           400  pulse                                                                             -200                                                                               100  1.97 75  200   1.9                                      Comparative                                                                          --   -- --  --   --   --  --    --                                       Example 1                                                                      Comparative                                                                          13.56                                                                               CW -200                                                                               100  1.7  85  200   1.9                                      Example 2                                                                      Comparative                                                                          1    CW -200                                                                               100  1.8  82  200   1.9                                      Example 3                                                                      Comparative                                                                          500  CW -200                                                                               100  1.8  81  200   1.9                                      Example 4                                                                      Comparative                                                                          20   CW -200                                                                               100  1.95 80  200   1.9                                      Example 5                                                                      Comparative                                                                          400  --   0 100  1.85 83  200   1.9                                      Example 6                                                                      Comparative                                                                          200  --   0 100  1.86 82  200   1.9                                      Example 7                                                                      Comparative                                                                          100  --   0 100  1.87 81  200   1.9                                      Example 8                                                                      Comparative                                                                          50   --   0 100  1.88 80  200   1.9                                      Example 9                                                                      Comparative                                                                          400  CW -200                                                                                20  1.95 77  200   1.9                                      Example 10                                                                     Comparative                                                                          400  CW -200                                                                               200  1.95 77  200   1.9                                      Example 11                                                                     Comparative                                                                          400  CW -200                                                                               100  1.95 77   50   1.9                                      Example 12                                                                     Comparative                                                                          400  CW -200                                                                               100  1.95 77  100   1.9                                      Example 13                                                                     Comparative                                                                          400  CW -200                                                                               100  1.95 77  200   1.5                                      Example 14                                                                     Comparative                                                                          400  CW -200                                                                               100  1.95 77  200   1.7                                      Example 15                                                                     Comparative                                                                          400  CW -200                                                                               100  1.95 77  200   2.0                                      Example 16                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               100  1.97 75  200   1.9                                      Example 17                                                                     Comparative                                                                    Example 18                                                                           400  pulse                                                                             -200                                                                               100  1.97 75  200   1.9                                      Comparative                                                                          --   -- --  --   --   --  --    --                                       Example 19                                                                     Comparative                                                                          400  CW -200                                                                               100  1.95 77  200   1.9                                      Example 20                                                                     Comparative                                                                          200  CW -200                                                                               100  1.95 77  200   1.9                                      Example 21                                                                     Comparative                                                                          100  CW -200                                                                               100  1.95 77  200   1.9                                      Example 22                                                                     Comparative                                                                          50   CW -200                                                                               100  1.95 77  200   1.9                                      Example 23                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               100  1.97 75  200   1.9                                      Example 24                                                                     Comparative                                                                          200  pulse                                                                             -200                                                                               100  1.98 75  200   1.9                                      Example 25                                                                     Comparative                                                                          100  pulse                                                                             -200                                                                               100  2.0  74  200   1.9                                      Example 26                                                                     Comparative                                                                          50   pulse                                                                             -200                                                                               100  2.1  73  200   1.9                                      Example 27                                                                     Comparative                                                                          400  CW -200                                                                               100  1.95 97  --                                             Example 28                                                                     Comparative                                                                          --   -- --  --   --   --  200   1.9                                      Example 29                                                                     __________________________________________________________________________                                Durable    Electro-                                                   Corrosion                                                                           Initial                                                                            Friction                                                                              Surface                                                                            magnetic                                       Liquid Lubricant                                                                       Still                                                                              Resistance                                                                          Friction                                                                           500 passes                                                                            Obser-                                                                             Charac-                                        Name of Material                                                                       (min)                                                                              (%)  (μ)                                                                             (μ) vation                                                                             teristics                                __________________________________________________________________________     Example 1                                                                            polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      ∘                            Example 2                                                                            polar PFPE                                                                             90  3    0.2 0.33   ∘                                                                      ∘                            Example 3                                                                            polar PFPE                                                                             90  3    0.2 0.32   ∘                                                                      ∘                            Example 4                                                                            polar PFPE                                                                             90  3    0.2 0.3    ∘                                                                      ∘                            Example 5                                                                            polar PFPE                                                                             >120                                                                               2    0.15                                                                               0.28   ∘                                                                      ∘                            Example 6                                                                            polar PFPE                                                                             >120                                                                               2    0.15                                                                               0.27   ∘                                                                      ∘                            Example 7                                                                            polar PFPE                                                                             >120                                                                               2    0.15                                                                               0,26   ∘                                                                      ∘                            Example 8                                                                            polar PFPE                                                                             >120                                                                               2    0.15                                                                               0.25   ∘                                                                      ∘                            Example 9                                                                            polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      ∘                            Example 10                                                                           polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      ∘                            Example 11                                                                           polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      ∘                            Example 12                                                                           polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      ∘                            Example 13                                                                           polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      ∘                            Example 14                                                                           polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      ∘                            Example 15                                                                           non-polar PFPE                                                                         90  3    0.2 0.34   ∘                                                                      ∘                            Example 16                                                                           PFA     90  3    0.2 0.34   ∘                                                                      ∘                            Example 17                                                                           phosphazene                                                                            90  3    0.2 0.34   ∘                                                                      ∘                            Example 18                                                                           non-polar PFPE                                                                         >120                                                                               2    0.15                                                                               0.28   ∘                                                                      ∘                            Example 19                                                                           PFA     >120                                                                               2    0.15                                                                               0.28   ∘                                                                      ∘                            Example 20                                                                           phosphazene                                                                            >120                                                                               2    0.15                                                                               0.28   ∘                                                                      ∘                            Comparative                                                                          polar PFPE                                                                             0.5 25   0.3 0.65   x   ∘                            Example 1                                                                      Comparative                                                                          polar PFPE                                                                             1   15   0.5 0.85   x   ∘                            Example 2                                                                      Comparative                                                                          polar PFPE                                                                             5   10   0.35                                                                               0.8    x   ∘                            Example 3                                                                      Comparative                                                                          polar PFPE                                                                             5   10   0.32                                                                               0.65   x   ∘                            Example 4                                                                      Comparative                                                                          polar PFPE                                                                             5   10   0.3 0.5    Δ                                                                            ∘                            Example 5                                                                      Comparative                                                                          polar PFPE                                                                             2   15   0.25                                                                               0.8    x   ∘                            Example 6                                                                      Comparative                                                                          polar PFPE                                                                             5   15   0.25                                                                               0.75   x   ∘                            Example 7                                                                      Comparative                                                                          polar PFPE                                                                             15  10   0.25                                                                               0.6    ∘                                Example 8                                                                      Comparative                                                                          polar PFPE                                                                             15  10   0.25                                                                               0.5    Δ                                                                            ∘                            Example 9                                                                      Comparative                                                                          polar PFPE                                                                             5   10   0.2 0.65   x   ∘                            Example 10                                                                     Comparative                                                                          polar PFPE                                                                             90  3    0.2 0.34   ∘                                                                      x                                        Example 11                                                                     Comparative                                                                          polar PFPE                                                                             90  10   0.2 0.65   x   ∘                            Example 12                                                                     Comparative                                                                          polar PFPE                                                                             90  10   0.2 0.65   x   ∘                            Example 13                                                                     Comparative                                                                          polar PFPE                                                                             10  15   0.2 0.65   x   ∘                            Example 14                                                                     Comparative                                                                          polar PFPE                                                                             10  10   0.2 0.65   x   ∘                            Example 15                                                                     Comparative                                                                          polar PFPE                                                                             5   15   0.2 0.3    x   ∘                            Example 16                                                                     Comparative                                                                          fatty acid                                                                             2   2    0.35                                                                               100 passes                                                                            x   ∘                            Example 17                                                                     Comparative                                                                          silicone oil                                                                           2   2    0.4 100 passes                                                                            x   ∘                            Example 18                                                                     Comparative                                                                          --      0.5 25   0.5 unmeasurable                                                                          x   ∘                            Example 19                                                                     Comparative                                                                          --      30  3    0.3 0.65   x   ∘                            Example 20                                                                     Comparative                                                                          --      30  3    0.3 0.65   x   ∘                            Example 21                                                                     Comparative                                                                          --      30  3    0.3 0.6 5  x   ∘                            Example 22                                                                     Comparative                                                                          --      30  3    0.3 0.65   x   ∘                            Example 23                                                                     Comparative                                                                          --      30  3    0.3 0.65   x   ∘                            Example 24                                                                     Comparative                                                                          --      30  3    0.3 0.65   x   ∘                            Example 25                                                                     Comparative                                                                          --      30  3    0.3 0.5    Δ                                                                            ∘                            Example 26                                                                     Comparative                                                                          --      30  3    0.3 0.5    Δ                                                                            ∘                            Example 27                                                                     Comparative                                                                          polar PFPE                                                                             30  15   0.25                                                                               0.34   ∘                                                                      ∘                            Example 28                                                                     Comparative                                                                          polar PFPE                                                                             0.5 15   0.25                                                                               0.65   x   ∘                            Example 29                                                                     __________________________________________________________________________

EXAMPLES 21 TO 42

SiOx (x=1.900) was plasma polymerized using a mixture of tetramethoxysilane and oxygen at a discharge frequency of 400 kHz to form an undercoat layer on a polyethylene terephthalate film substrate having a thickness of 7 μm, and an alloy containing 80% by weight of Co and 20% by weight of Ni was deposited thereon under an oxygen atmosphere to form a ferromagnetic metal layer (with a film thickness of 1,500 Å). Each of the various hydrocarbons shown in Tables 2-1 and 2-2 was plasma polymerized to form a protective layer. Further, using a polar perfluoropolyether (PFPE) as a liquid lubricant, a lubricating layer was formed.

The film thickness of the SiOx undercoat layers, the kinds of hydrocarbons, the plasma frequency and the bias on film formation, and the film thickness, the refractive index and the contact angle of the resulting protective layers are shown in Tables 2-1 and 2-2. Further, for the resulting magnetic recording tapes, the still time, the corrosion resistance, the initial friction, the durable friction, the results of surface observation and the electromagnetic characteristics are shown in Tables 2-3 and 2-4.

The film thickness, the refractive index, the composition of SiOx and the contact angle were measured in the same manner as with Examples 1 to 20.

                                      TABLE 2                                      __________________________________________________________________________                                           Undercoat layer                          Protective Film (DLC Film)            (SiOx)                                         Plasma      Film                Film                                           Frequency   Thickness                                                                           Raw Mate-                                                                            Refract-                                                                            Contact                                                                            Thickness                                                                           Value                                     (kHz)                                                                               Bias                                                                              Bias V                                                                             (Å)                                                                             rial Gas                                                                             ive Index                                                                           Angle                                                                              (Å)                                                                             of x                                __________________________________________________________________________     Example 21                                                                           400  CW -200                                                                               100  methane/H2                                                                           1.95 77  200  1.9                                 Example 22                                                                           400  pulse                                                                             -200                                                                               100  methane/H2                                                                           1.97 75  200  1.9                                 Example 23                                                                           400  CW -200                                                                               100  ethane                                                                               1.95 77  200  1.9                                 Example 24                                                                           400  CW -200                                                                               100  ethane/H2                                                                            1.95 77  200  1.9                                 Example 25                                                                           400  pulse                                                                             -200                                                                               100  ethane                                                                               1.97 75  200  1.9                                 Example 26                                                                           400  pulse                                                                             -200                                                                               100  ethane/H2                                                                            1.97 75  200  1.9                                 Example 27                                                                           400  CW -200                                                                               100  propane                                                                              1.95 77  200  1.9                                 Example 28                                                                           400  CW -200                                                                               100  propane/H2                                                                           1.95 77  200  1.9                                 Example 29                                                                           400  pulse                                                                             -200                                                                               100  propane                                                                              1.97 75  200  1.9                                 Example 30                                                                           400  pulse                                                                             -200                                                                               100  propane/H2                                                                           1.97 75  200  1.9                                 Example 31                                                                           400  CW -200                                                                               100  butane                                                                               1.95 77  200  1.9                                 Example 32                                                                           400  CW -200                                                                               100  butane/H2                                                                            1.95 77  200  1.9                                 Example 33                                                                           400  pulse                                                                             -200                                                                               100  butane                                                                               1.97 75  200  1.9                                 Example 34                                                                           400  pulse                                                                             -200                                                                               100  butane/H2                                                                            1.97 75  200  1.9                                 Example 35                                                                           400  CW -200                                                                               100  ethylene                                                                             1.97 76  200  1.9                                 Example 36                                                                           400  CW -200                                                                               100  ethylene/H2                                                                          1.97 76  200  1.9                                 Example 37                                                                           400  pulse                                                                             -200                                                                               100  ethylene                                                                             2.0  74  200  1.9                                 Example 38                                                                           400  pulse                                                                             -200                                                                               100  ethylene/H2                                                                          2.0  74  200  1.9                                 Example 39                                                                           400  CW -200                                                                               100  acetylene                                                                            1.97 76  200  1.9                                 Example 40                                                                           400  CW -200                                                                               100  acetylene/H2                                                                         1.97 76  200  1.9                                 Example 41                                                                           400  pulse                                                                             -200                                                                               100  acetylene                                                                            2.0  74  200  1.9                                 Example 42                                                                           400  pulse                                                                             -200                                                                               100  acetylene/H2                                                                         2.0  74  200  1.9                                 __________________________________________________________________________                                   Durable   Electro-                                                   Corrosion                                                                            Initial                                                                            Friction                                                                             Surface                                                                            magnetic                                     Liquid Lubricant                                                                        Still                                                                               Resistance                                                                           Friction                                                                           500 passes                                                                           Obser-                                                                             Charac-                                      Name of Material                                                                        (min)                                                                               (%)   (μ)                                                                             (μ)                                                                               vation                                                                             teristics                              __________________________________________________________________________     Example 21                                                                           polar PFPE                                                                                90 3     0.2 0.34  ∘                                                                      ∘                          Example 22                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 23                                                                           polar PFPE                                                                                90 3     0.2 0.34  ∘                                                                      ∘                          Example 24                                                                           polar PFPE                                                                                90 3     0.2 0.34  ∘                                                                      ∘                          Example 25                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 26                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 27                                                                           polar PFPE                                                                                90 3     0.21                                                                               0.34  ∘                                                                      ∘                          Example 28                                                                           polar PFPE                                                                                90 3     0.2i                                                                               0.34  ∘                                                                      ∘                          Example 29                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 30                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                              Example 31                                                                           polar PFPE                                                                                90 3     0.22                                                                               0.35  ∘                                                                      ∘                          Example 32                                                                           polar PFPE                                                                                90 3     0.22                                                                               0.34  ∘                                                                      ∘                          Example 33                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 34                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 35                                                                           polar PFPE                                                                               100 2     0.18                                                                               0.3   ∘                                                                      ∘                          Example 36                                                                           polar PFPE                                                                               100 2     0.19                                                                               0.3   ∘                                                                      ∘                          Example 37                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 38                                                                           polar PFPE                                                                              >120 2     0.15                                                                               0.28  ∘                                                                      ∘                          Example 39                                                                           polar PFPE                                                                               100 3     0.16                                                                               0.3   ∘                                                                      ∘                          Example 40                                                                           polar PFPE                                                                               100 3     0.16                                                                               0.3   ∘                                                                      ∘                          Example 41                                                                           polar PFPE                                                                              >120 2     0.14                                                                               0.25  ∘                                                                      ∘                          Example 42                                                                           polar PFPE                                                                              >120 2     0.14                                                                               0.25  ∘                                                                      ∘                          __________________________________________________________________________

EXAMPLE 43 TO 57 AND COMPARATIVE EXAMPLES 30 TO 36

Magnetic recording media were produced in the same manner as with the above-mentioned Examples, with the exception that CW and a pulse bias were used as the negative bias, and the pulse frequency Hz, the flow ratio of CH₄ /H and the pulse ratio ON/OFF were variously changed. The pulse ratio was changed by setting the ON/OFF time with a setting switch attached to a power supply.

Results are shown in the following Tables 3-1 to 3-4.

                                      TABLE 3                                      __________________________________________________________________________           Plasma      Flow Pulse                                                                               Pulse                                                                               Film                                                Frequency   Ratio                                                                               Ratio                                                                               Frequency                                                                           Thickness                                                                           Refract-                                                                            Contact                                   (kHz)                                                                               Bias                                                                              Bias V                                                                             (CH.sub.4 /H.sub.2)                                                                 (ON/OFF)                                                                            Hz   (Å)                                                                             ive Index                                                                           Angle                               __________________________________________________________________________     Example 43                                                                           400  CW -200                                                                               1/3  --   --   100  1.95 77                                  Example 44                                                                           400  CW -200                                                                               1/2  --   --   100  1.95 77                                  Example 45                                                                           400  CW -200                                                                               2/1  --   --   100  1.95 77                                  Example 46                                                                           400  CW -200                                                                               3/1  --   --   100  1.95 77                                  Example 47                                                                           400  pulse                                                                             -200                                                                               1/1  1/3   50  100  1.95 79                                  Example 48                                                                           400  pulse                                                                             -200                                                                               1/1  1/2   50  100  1.95 77                                  Example 49                                                                           400  pulse                                                                             -200                                                                               1/1  2/1   50  100  1.95 77                                  Example 50                                                                           400  pulse                                                                             -200                                                                               1/1  3/1   50  100  1.95 77                                  Example 51                                                                           400  pulse                                                                             -200                                                                               1/1  1/1   10  100  1.95 79                                  Example 52                                                                           400  pulse                                                                             -200                                                                               1/1  1/1   20  100  1.95 77                                  Example 53                                                                           400  pulse                                                                             -200                                                                               1/1  1/1  100  100  1.95 77                                  Example 54                                                                           400  pulse                                                                             -200                                                                               1/1  1/1  200  100  1.95 77                                  Example 55                                                                           400  pulse                                                                             -200                                                                               1/1  1/1  300  100  1.95 77                                  Example 56                                                                           400  pulse                                                                             -200                                                                               1/1  1/1  400  100  1.95 77                                  Example 57                                                                           400  pulse                                                                             -200                                                                               1/1  1/1  500  100  1.95 77                                  Comparative                                                                          400  CW -200                                                                               1/4  --   --   100  1.88 80                                  Example 30                                                                     Comparative                                                                          400  CW -200                                                                               4/1  --   --   100  1.9  80                                  Example 31                                                                     Compardtive                                                                          400  pulse                                                                             -200                                                                               1/1  4/1   50  100  1.88 77                                  Example 32                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/4   50  100  1.85 82                                  Example 33                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/1   5   100  1.88 80                                  Example 34                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  600  100  1.8  81                                  Example 35                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  1000 100  1.8  81                                  Example 36                                                                     __________________________________________________________________________                           Durable                                                             Corrosion                                                                             Initial                                                                            Friction                                                        Still                                                                              Resistance                                                                            Friction                                                                           500 passes                                                                              Surface                                                                              Electromagnetic                                  (min)                                                                              (%)    (μ)                                                                             (μ)   Observation                                                                          Characteristics                           __________________________________________________________________________     Example 43                                                                             90 3      0.25                                                                               0.34     ∘                                   Example 44                                                                             90 3      0.25                                                                               0.34     ∘                                                                        ∘                             Example 45                                                                             90 3      0.25                                                                               0.34     ∘                                                                        ∘                             Example 46                                                                             90 3      0.25                                                                               0.34     ∘                                                                        ∘                             Example 47                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 48                                                                            120 2      0.2 0.34     ∘                                                                        ∘                             Example 49                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 50                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 51                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 52                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 53                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 54                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 55                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 56                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Example 57                                                                            120 2      0.2 0.35     ∘                                                                        ∘                             Comparative                                                                            10 5      0.3 0.7      x     x                                         Example 30                                                                     Comparative                                                                            10 10     0.3 0.5      Δ                                                                              x                                         Example 31                                                                     Comparative                                                                            30 10     0.25                                                                               0.55     x     x                                         Example 32                                                                     Comparative                                                                            5  10     0.3 0.7      x     x                                         Example 33                                                                     Comparative                                                                            10 5      0.3 0.9      x     x                                         Example 34                                                                     Comparative                                                                            5  10     0.32                                                                               0.6      x     x                                         Example 35                                                                     Comparative                                                                            5  10     0.32                                                                               0.6      x     x                                         Example 36                                                                     __________________________________________________________________________

B. Magnetic Recording Media of (2)

EXAMPLES 58 TO 85 AND COMPARATIVE EXAMPLES 37 TO 65

The inside of a chamber was evacuated to 10⁻⁶ Torr, and then tetramethoxysilane as a raw material and oxygen were introduced thereinto at a ratio of 1:3, followed by adjustment of the pressure to 10⁻² Torr. Then, an audio frequency of 100 kHz was applied to an electrode to generate plasma discharges and to plasma polymerize SiOx having each of the various compositions shown in Tables 4-1 to 4-6, thereby forming an undercoat layer on a polyethylene terephthalate film substrate having a thickness of 7 μm. Subsequently, an alloy containing 80% by weight of Co and 20% by weight of Ni was deposited under an oxygen atmosphere to form a ferromagnetic metal layer (with a film thickness of 1,500 Å), and SiOx having each of the various compositions shown in Tables 4-1 to 4-6 was plasma polymerized thereon in a manner similar to that described above to form a intercepting layer. The x value in the SiOx film was changed by varying the ratio of oxygen introduced together with the silane series organic compound.

Then, a protective layer was formed thereon by plasma polymerization using methane as a hydrocarbon source by use of a DLC film producing apparatus such as shown in FIG. 1. Namely, the inside of a chamber was evacuated to 10⁻⁶ Torr, and then methane as a raw material and hydrogen were introduced thereinto at a ratio of 1:1, followed by adjustment of the pressure to 10⁻² Torr. Thereafter, electromagnetic waves were applied to electrodes at high frequency to generate plasma discharges. At the same time, a DC bias was applied connecting as shown in FIG. 1. As the DC bias on the base side, one having a pulse generation mechanism was used.

The protective layer was further coated by gravure coating with a solution prepared by dissolving each of the various lubricants shown in Tables 7 to 12 in a solvent, EFL-150 (Daikin Kogyo Co.), in a concentration of 0.3% by weight, thereby forming a lubricating layer. The film thickness was about 40 Å.

S20 (Daikin Kogyo Co.) was used as a non-polar perfluoro-polyether (PFPE), KF-851 (Shinetsu Kagaku Kogyo Co.) as silicone oil, SAl (Daikin Kogyo Co.) as a polar PFPE, n-C₁₀ F₂₀ COOH as a perfluorocarboxylic acid (PFA), phosphazene (Idemitsu Sekiyu Kagaku Co.) as a phosphazene, FA108 as a perfluoroacrylate, and n-C₁₀ F₂₀ COOC₁₀ F₂₀ as a perfluoroalkylate. The composition and the film thickness of the SiOx undercoat layers, the plasma frequency and the bias on film formation of the hydrogen-containing carbon film protective layers, and the film thickness, the refractive index and the contact angle of the resulting protective layers are shown in Tables 4-1 to 4-6. When the pulse bias is used, the pulse is 50 Hz. Further, for the resulting magnetic recording tapes, the materials of the lubricating layers, the still time, the corrosion resistance, the initial friction, the durable friction, the results of surface observation and the electromagnetic characteristics are shown in Tables 4-7 to 4-12.

The film thickness and the refractive index were measured by ellipsometry. The composition of SiOx was measured by ESCA. The contact angle was measured by a droplet dropping system using a contact angle meter (Kyowa Kaimen Kagaku Co.). For comparison, protective layers were formed using RF and 1 MHz.

                                      TABLE 4                                      __________________________________________________________________________                                  Intercepting Film                                                                       Undercoat layer                          Protective Film (DLC Film)   (SiOx Film)                                                                             (SiOx Film)                                    Plasma     Film        Film     Film                                           Fre-       Thick-                                                                             Refrac- Thick-   Thick-                                         quency Bias                                                                               ness                                                                               tive                                                                               Contact                                                                            ness                                                                               Value                                                                               ness                                                                               Value                                      (kHz)                                                                              Bias                                                                              V   (Å)                                                                            Index                                                                              Angle                                                                              (Å)                                                                            of x (Å)                                                                            of x                                 __________________________________________________________________________     Example 58                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 59                                                                           200 CW -200                                                                               50  1.97                                                                               77  50  1.90 200 1.90                                 Example 60                                                                           100 CW -200                                                                               50  1.98                                                                               76  50  1.90 200 1.90                                 Example 61                                                                           50  CW -200                                                                               50  2.0 75  50  1.90 200 1.90                                 Example 62                                                                           400 pulse                                                                             -200                                                                               50  1.97                                                                               75  50  1.90 200 1.90                                 Example 63                                                                           200 pulse                                                                             -200                                                                               50  1.98                                                                               75  50  1.90 200 1.90                                 Example 64                                                                           100 pulse                                                                             -200                                                                               50  2.0 74  50  1.90 200 1.90                                 Example 65                                                                           50  pulse                                                                             -200                                                                               50  2.1 73  50  1.90 200 1.90                                 Example 66                                                                           400 CW -200                                                                               30  1.95                                                                               77  50  1.90 200 1.90                                 Example 67                                                                           400 CW -200                                                                               80  1.95                                                                               77  50  1.90 200 1.90                                 Example 68                                                                           400 CW -200                                                                               50  1.95                                                                               77  30  1.90 200 1.90                                 Example 69                                                                           400 CW -200                                                                               50  1.95                                                                               77  80  1.90 200 1.90                                 Example 70                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.80 200 1.90                                 Example 71                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.95 200 1.90                                 Example 72                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 150 1.90                                 Example 73                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 150 1.90                                 Example 74                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 75                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.95                                 Example 76                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 77                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 78                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 79                                                                           400 pulse                                                                             -200                                                                               50  1.97                                                                               75  50  1.90 200 1.90                                 Example 80                                                                           400 pulse                                                                             -200                                                                               50  1.97                                                                               75  50  1.90 200 1.90                                 Example 81                                                                           400 pulse                                                                             -200                                                                               50  1.97                                                                               75  50  1.90 200 1.90                                 Example 82                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 83                                                                           400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 84                                                                           400 CW -200                                                                               50  1.95                                                                               77  100 1.90 200 1.90                                 Example 85                                                                           400 CW -200                                                                               100 1.95                                                                               77  50  1.90 200 1.90                                 Comparative                                                                          13.51                                                                              CW -200                                                                               50  1.70                                                                               85  50  1.90 200 1.90                                 Example 37                                                                     Comparative                                                                          1   CW -200                                                                               50  1.80                                                                               82  50  1.90 200 1.90                                 Example 38                                                                     Comparative                                                                          500 CW -200                                                                               50  1.80                                                                               81  50  1.90 200 1.90                                 Example 39                                                                     Comparative                                                                          20  CW -200                                                                               50  1.95                                                                               80  50  1.90 200 1.90                                 Example 40                                                                     Comparative                                                                          400 -- 0   50  1.85                                                                               83  50  1.90 200 1.90                                 Example 41                                                                     Comparative                                                                          200 -- 0   50  1.86                                                                               82  50  1.90 200 1.90                                 Example 42                                                                     Comparative                                                                          100 -- 0   50  1.87                                                                               81  50  1.90 200 1.90                                 Example 43                                                                     Comparative                                                                          50  -- 0   50  1.88                                                                               80  50  1.90 200 1.90                                 Example 44                                                                     Comparative                                                                          400 CW -200                                                                               20  1.95                                                                               77  50  1.90 200 1.90                                 Example 45                                                                     Comparative                                                                          400 CW -200                                                                               100 1.95                                                                               77  100 1.90 200 1.90                                 Example 46                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  20  1.90 200 1.90                                 Example 47                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.50 200 1.90                                 Example 48                                                                     Comparative                                                                          400 CW -2 00                                                                              50  1.95                                                                               77  50  1.70 200 1.90                                 Example 49                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  2.0  200 1.90                                 Example 50                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 100 1.90                                 Example 51                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.50                                 Example 52                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.70                                 Example 53                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 2.00                                 Example 54                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 55                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 1.90                                 Example 56                                                                     Comparative                                                                    Example 57                                                                     Comparative                                                                    Example 58                                                                           --  -- --  --  --  --  --  --   --  --                                   Comparative                                                                          --  -- --  --  --  --  50  1.90 200 1.90                                 Example 59                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  --  --   200 1.90                                 Example 60                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90                                          Example 61                                                                     Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  SiO.sub.2                                                                           200 1.90                                 Example 62                       deposition                                    Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 SiO.sub.2                            Example 63                                deposition                           Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  SiO.sub.2                                                                           200 1.90                                 Example 64                       deposition                                    Comparative                                                                          400 CW -200                                                                               50  1.95                                                                               77  50  1.90 200 SiO.sub.2                            Example 65                                deposition                           __________________________________________________________________________                                        Durable                                                                               Electro-                                           Still                                                                              Still   Corrosion                                                                           Initial                                                                            Friction                                                                              magnetic                                   Liquid Lubricant                                                                       -1 dB                                                                              -5 dB                                                                              Scratch                                                                            Resistance                                                                          Friction                                                                           200 passes                                                                            Charac-                                    Name of Material                                                                       (min)                                                                              (min)                                                                              (mN)                                                                               (%)  (μ)                                                                             (μ) teristics                            __________________________________________________________________________     Example 58                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 59                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 60                                                                           polar PFPE                                                                             100 >120                                                                               80  1    0.25                                                                               0.40   ∘                        Example 61                                                                           polar PFPE                                                                             100 >120                                                                               80  1    0.25                                                                               0.40   ∘                        Example 62                                                                           polar PFPE                                                                             >120                                                                               >120                                                                               120 1    0.15                                                                               0.20   ∘                        Example 63                                                                           polar PFPE                                                                             >120                                                                               >120                                                                               120 1    0.15                                                                               0.20   ∘                        Example 64                                                                           polar PFPE                                                                             >120                                                                               >120                                                                               120 1    0.15                                                                               0.20   ∘                        Example 65                                                                           polar PFPE                                                                             >120                                                                               >120                                                                               120 1    0.15                                                                               0.20   ∘                        Example 66                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 67                                                                           polar PFPE                                                                             100 >120                                                                               80  1    0.25                                                                               0.40   ∘                        Example 68                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 69                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 70                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 71                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 72                                                                           polar PFPE                                                                             70  100 75  5    0.25                                                                               0.45   ∘                        Example 73                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 74                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 75                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 76                                                                           non-polar PFPE                                                                         90  120 80  1    0.25                                                                               0.40   ∘                        Example 77                                                                           PFA     90  120 80  1    0.20                                                                               0.40   ∘                        Example 78                                                                           phosphazene                                                                            90  120 80  1    0.25                                                                               0.38   ∘                        Example 79                                                                           non-polar PFPE                                                                         >120                                                                               >120                                                                               80  1    0.15                                                                               0.20   ∘                        Example 80                                                                           PFA     >120                                                                               >120                                                                               80  1    0.15                                                                               0.20   ∘                        Example 81                                                                           phosphazene                                                                            >120                                                                               >120                                                                               80  1    0.15                                                                               0.20   ∘                        Example 82                                                                           FA108   90  120 80  1    0.25                                                                               0.40   ∘                        Example 83                                                                           alkylate                                                                               90  120 80  1    0.20                                                                               0.40   ∘                        Example 84                                                                           polar PFPE                                                                             90  120 80  1    0.25                                                                               0.40   ∘                        Example 85                                                                           polar PFPE                                                                             90  >120                                                                               80  1    0.25                                                                               0.40   ∘                        Comparative                                                                          polar PFPE                                                                             0.5 1   10  13   0.50                                                                               0.85   ∘                        Example 37                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  10   0.35                                                                               0.80   ∘                        Example 38                                                                     Comparative                                                                          polar PFPE                                                                             3   5   25  10   0.32                                                                               0.60   ∘                        Example 39                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  10   0.30                                                                               0.50   ∘                        Example 40                                                                     Comparative                                                                          polar PFPE                                                                             1   2   15  12   0.35                                                                               0.80   ∘                        Example 41                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  10   0.30                                                                               0.50   ∘                        Example 42                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  10   0.30                                                                               0.50   ∘                        Example 43                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  10   0.30                                                                               0.50   ∘                        Example 44                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  10   0.35                                                                               0.60   ∘                        Example 45                                                                     Comparative                                                                          polar PFPE                                                                             100 >120                                                                               80  1    0.25                                                                               0.40   x                                    Example 46                                                                     Comparative                                                                          polar PFPE                                                                             30  45  40  5    0.25                                                                               0.60   ∘                        Example 47                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  12   0.25                                                                               0.60   ∘                        Example 48                                                                     Comparative                                                                          polar PFPE                                                                             3   5   25  11   0.25                                                                               0.50   ∘                        Example 49                                                                     Comparative                                                                          polar PFPE                                                                             1   2   15  15   0.25                                                                               0.65   ∘                        Example 50                                                                     Comparative                                                                          polar PFPE                                                                             30  45  35  17   0.25                                                                               0.55   ∘                        Example 51                                                                     Comparative                                                                          polar PFPE                                                                             5   10  20  17   0.25                                                                               0.65   ∘                        Example 52                                                                     Comparative                                                                          polar PFPE                                                                             5   10  25  15   0.25                                                                               0.60   ∘                        Example 53                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  17   0.25                                                                               0.80   ∘                        Example 54                                                                     Comparative                                                                          fatty acid                                                                             1   2   80  1    0.35                                                                               100 passes                                                                            ∘                        Example 55                         stop                                        Comparative                                                                          silicone oil                                                                           1   2   80  1    0.40                                                                               100 passes                                                                            ∘                        Example 56                         stop                                        Comparative                                                                          --      0.5 0.5 --  25   0.50                                                                               unmeasurable                                                                          ∘                        Example 57                                                                     Comparative                                                                          polar PFPE                                                                             0.5 0.5 --  25   0.30                                                                               0.60   ∘                        Example 58                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  10   0.30                                                                               0.50   ∘                        Example 59                                                                     Comparative                                                                          polar PFPE                                                                             3   5   20  5    0.30                                                                               0.50   ∘                        Example 60                                                                     Comparative                                                                          polar PFPE                                                                             30  45  20  10   0.25                                                                               0.60   ∘                        Example 61                                                                     Comparative                                                                          polar PFPE                                                                             5   20  20  10   0.30                                                                               100 passes                                                                            ∘                        Example 62                         stop                                        Comparative                                                                          polar PFPE                                                                             5   20  20  10   0.30                                                                               100 passes                                                                            ∘                        Example 63                         stop                                        Comparative                                                                          polar PFPE                                                                             10  30  20  10   0.30                                                                               150 passes                                                                            ∘                        Example 64                         stop                                        Comparative                                                                          polar PFPE                                                                             10  30  20  10   0.30                                                                               150 passes                                                                            ∘                        Example 65                         stop                                        __________________________________________________________________________

EXAMPLES 86 TO 107

SiOx (x=1.900) was plasma polymerized using a mixture of tetramethoxysilane and oxygen at a discharge frequency of 400 kHz to form an undercoat layer on a polyethylene terephthalate film substrate having a thickness of 71 μm, and an alloy containing 80% by weight of Co and 20% by weight of Ni was deposited thereon under an oxygen atmosphere to form a ferromagnetic metal layer (with a film thickness of 1,500 Å). Then, SiOx (x=1.900) was plasma polymerized to form an intercepting layer, and each of the various hydrocarbons shown in Tables 5-1 and 5-2 was plasma polymerized thereon to form a protective layer. Further, using a polar perfluoropolyether (PFPE) as a liquid lubricant, a lubricating layer was formed. The film thickness of the intercepting layers, the kinds of hydrocarbons, the plasma frequency and the bias on film formation, and the film thickness, the refractive index and the contact angle of the resulting protective layers are shown in Tables 5-1 and 5-2, and the film thickness of the SiOx undercoat layers is shown in Tables 5-3 and 5-4. Further, for the resulting magnetic recording tapes, the still time, the corrosion resistance, the initial friction, the durable friction and the results of surface observation are shown in Tables 5-3 and 5-4.

The film thickness, the refractive index, the composition of SiOx and the contact angle were measured in the same manner as with Examples 38 to 61.

                                      TABLE 5                                      __________________________________________________________________________                                           Intercepting                             Protective Film (DLC Film)            Film (SiOx)                                    Plasma      Film                Film                                           Frequency   Thickness                                                                           Refrac-                                                                             Contact                                                                            Raw Mate-                                                                            Thickness                                                                           Value                                     (kHz)                                                                               Bias                                                                              Bias V                                                                             (Å)                                                                             tive Index                                                                          Angle                                                                              rial Gas                                                                             (Å)                                                                             of x                                __________________________________________________________________________     Example 86                                                                           400  CW -200                                                                               50   1.95 77  methane/H2                                                                           50   1.90                                Example 87                                                                           400  pulse                                                                             -200                                                                               50   1.97 75  methane/H2                                                                           50   1.90                                Example 88                                                                           400  CW -200                                                                               50   1.95 77  ethane                                                                               50.  1.90                                Example 89                                                                           400  CW -200                                                                               50   1.95 77  ethane/H2                                                                            50   1.90                                Example 90                                                                           400  pulse                                                                             -200                                                                               50   1.97 75  ethane                                                                               50   1.90                                Example 91                                                                           400  pulse                                                                             -200                                                                               50   1.97 75  ethane/H2                                                                            50   1.90                                Example 92                                                                           400  CW -200                                                                               50   1.95 77  propane                                                                              50   1.90                                Example 93                                                                           400  CW -200                                                                               50   1.95 77  propane/H2                                                                           50   1.90                                Example 94                                                                           400  pulse                                                                             -200                                                                               50   1.97 75  propane                                                                              50   1.90                                Example 95                                                                           400  pulse                                                                             -200                                                                               50   1.97 75  propane/H2                                                                           50   1.90                                Example 96                                                                           400  CW -200                                                                               50   1.95 77  butane                                                                               50   1.90                                Example 97                                                                           400  CW -200                                                                               50   1.95 77  butane/H2                                                                            50   1.90                                Example 98                                                                           400  pulse                                                                             -200                                                                               50   1.97 75  butane                                                                               50   1.90                                Example 99                                                                           400  pulse                                                                             -200                                                                               50   1.99 75  butane/H2                                                                            50   1.90                                Example 100                                                                          400  CW -200                                                                               50   1.97 76  ethylene                                                                             50   1.90                                Example 101                                                                          400  CW -200                                                                               50   1.97 76  ethylene/H2                                                                          50   1.90                                Example 102                                                                          400  pulse                                                                             -200                                                                               50   2.0  74  ethylene                                                                             50   1.90                                Example 103                                                                          400  pulse                                                                             -200                                                                               50   2.0  74  ethylene/H2                                                                          50   1.90                                Example 104                                                                          400  CW -200                                                                               50   1.97 76  acetylene                                                                            50   1.90                                Example 105                                                                          400  CW -200                                                                               50   1.97 76  acetylene/H2                                                                         50   1.90                                Example 106                                                                          400  pulse                                                                             -200                                                                               50   2.0  74  acetylene                                                                            50   1.90                                Example 107                                                                          400  pulse                                                                             -200                                                                               50   2.0  74  acetylene/H2                                                                         50   1.90                                __________________________________________________________________________     Undercoat                                                                      layer (SiOx)                     Corro-                                              Film                       sion    Durable                                     Thick-         Still                                                                              Still   Resis-                                                                             Initial                                                                            Friction                                    ness                                                                               Value                                                                             Liquid Lubricant                                                                       -1 dB                                                                              -5 dB                                                                              Scratch                                                                            tance                                                                              Friction                                                                           200 passes                                  (Å)                                                                            of x                                                                              Name of Material                                                                       (min)                                                                              (min)                                                                              (mN)                                                                               (%) (μ)                                                                             μ)                                 __________________________________________________________________________     Example 86                                                                           200 1.90                                                                              polar PFPE                                                                              100                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 87                                                                           200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 88                                                                           200 1.90                                                                              polar PFPE                                                                              100                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 89                                                                           200 1.90                                                                              polar PFPE                                                                              100                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 90                                                                           200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 91                                                                           200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 92                                                                           200 1.90                                                                              polar PFPE                                                                              100                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 93                                                                           200 1.90                                                                              polar PFPE                                                                              100                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 94                                                                           200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 95                                                                           200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 96                                                                           200 1.90                                                                              polar PFPE                                                                              100                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 97                                                                           200 1.90                                                                              polar PFPE                                                                              100                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 98                                                                           200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 99                                                                           200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 100                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 101                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 102                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 103                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 104                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 105                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 106                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  Example 107                                                                          200 1.90                                                                              polar PFPE                                                                             >120                                                                               >120                                                                               80  1   0.15                                                                               0.20                                  __________________________________________________________________________

EXAMPLES 108 TO 122 AND COMPARATIVE EXAMPLES 66 TO 72

Magnetic recording media were produced in the same manner as with the above-mentioned Examples, with the exception that CW and a pulse bias were used as the negative bias, and the pulse frequency Hz, the flow ratio of CH₄ /H and the pulse ratio ON/OFF were variously changed. The pulse ratio was changed by setting the ON/OFF time with a setting switch attached to a power supply.

Results are shown in the following Tables 6-1 to 6-4.

                                      TABLE 6                                      __________________________________________________________________________           Plasma      Flow Pulse                                                                               Pulse                                                                               Film                                                Frequency   Ratio                                                                               Ratio                                                                               Frequency                                                                           Thickness                                                                           Refract-                                                                            Contact                                   (kHz)                                                                               Bias                                                                              Bias V                                                                             (CH.sub.4 /H.sub.2)                                                                 (ON/OFF)                                                                            Hz   (Å)                                                                             ive Index                                                                           Angle                               __________________________________________________________________________     Example 108                                                                          400  CW -200                                                                               1/3  --   --   50   1.95 77                                  Example 109                                                                          400  CW -200                                                                               1/2  --   --   50   1.95 77                                  Example 110                                                                          400  CW -200                                                                               2/1  --   --   50   1.95 77                                  Example 111                                                                          400  CW -200                                                                               3/1  --   --   50   1.95 77                                  Example 112                                                                          400  pulse                                                                             -200                                                                               1/1  1/3   50  50   1.95 77                                  Example 113                                                                          400  pulse                                                                             -200                                                                               1/1  1/2   50  50   1.95 77                                  Example 114                                                                          400  pulse                                                                             -200                                                                               1/1  2/1   50  50   1.95 77                                  Example 115                                                                          400  pulse                                                                             -200                                                                               1/1  3/1   50  50   1.95 77                                  Example 116                                                                          400  pulse                                                                             -200                                                                               1/1  1/1   10  50   1.95 77                                  Example 119                                                                          400  pulse                                                                             -200                                                                               1/1  1/1   20  50   1.95 77                                  Example 118                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  100  50   1.95 77                                  Example 119                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  200  50   1.95 77                                  Example 120                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  300  50   1.95 77                                  Ekample 121                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  400  50   1.95 77                                  Example 122                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  500  50   1.95 77                                  Comparative                                                                          400  CW -200                                                                               1/4  --   --   50   1.88 80                                  Example 66                                                                     Comparative                                                                          400  CW -200                                                                               4/1  --   --   50   1.9  80                                  Example 67                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  4/1   50  50   1.88 77                                  Example 68                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/4   50  50   1.85 82                                  Example 69                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/1   5   50   1.88 80                                  Example 70                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  600  50   1.8  81                                  Example 71                                                                     Comparative                                                                          400  pulse                                                                             -200                                                                               1/1  1/1  1000 50   1.8  81                                  Example 72                                                                     __________________________________________________________________________                                Durable                                                   Still Still                                                                              Corrosion                                                                             Initial                                                                            Friction                                                  -1 dB -5 dB                                                                              Resistance                                                                            Friction                                                                           200 passes                                                                            Scratch                                                                            Electromagnetic                                (min) (min)                                                                              (%)    (μ)                                                                             (μ) (mN)                                                                               Characteristics                          __________________________________________________________________________     Example 108                                                                           120   90 3      0.25                                                                               0.34    80 ∘                            Example 109                                                                           120   90 3      0.25                                                                               0.34    80 ∘                            Example 110                                                                           120   90 3      0.25                                                                               0.34    80 ∘                            Example 111                                                                           120   90 3      0.25                                                                               0.34    80 ∘                            Example 112                                                                          >120  120 2      0.2 0.35    90 ∘                            Example 113                                                                          >120  120 2      0.2 0.34   100 ∘                            Example 114                                                                          >120  120 2      0.2 0.35   120 ∘                            Example 115                                                                          >120  120 2      0.2 0.35   120 ∘                            Example 116                                                                          >120  120 2      0.2 0.35    90 ∘                            Example 117                                                                          >120  120 2      0.2 0.35   100 ∘                            Example 118                                                                          >120  120 2      0.2 0.35   120 ∘                            Example 119                                                                          >120  120 2      0.2 0.35   120 ∘                            Example 120                                                                          >120  120 2      0.2 0.35   120 ∘                            Example 121                                                                          >120  120 2      0.2 0.35   120 ∘                            Example 122                                                                          >120  120 2      0.2 0.35   120 ∘                            Comparative                                                                            30   10 5      0.3 0.7     25 x                                        Example 66                                                                     Comparative                                                                            30   10 10     0.3 0.5     25 x                                        Example 67                                                                     Comparative                                                                            10   30 10     0.25                                                                               0.55    25 x                                        Example 68                                                                     Comparative                                                                            30   5  10     0.3 0.7     20 x                                        Example 69                                                                     Comparative                                                                            20   10 5      0.3 0.7     20 x                                        Example 70                                                                     Comparative                                                                            20   5  10     0.32                                                                               0.6     20 x                                        Example 71                                                                     Comparative                                                                            20   5  10     0.32                                                                               0.6     20 x                                        Example 72                                                                     __________________________________________________________________________

In the magnetic recording medium of the present invention having the ferromagnetic metal layer serving as the magnetic layer, the specified silicon oxide films are used as the undercoat layer and the insulating layer for the magnetic layer, the plasma-polymerized hydrogen-containing carbon film, plasma polymerized under the specified applying conditions and having the specified characteristics, is used as the protective layer, and the lubricating layer is formed of the specified fluorine compound, thereby providing the magnetic recording medium with excellent electromagnetic characteristics, corrosion resistance, durability, abrasion resistance and lubricity.

By the combination of the foregoing and the contact angle of the protective, as formed, being less than 80°, as set forth in the following claims, the present invention has excellent effect in the still durability. This is shown in Table 1, especially Tables 1-6 to 1-10, and Comparative Examples 2 to 9. In addition to the still durability, the present invention has better effect in initial friction and durable friction as compared to a magnetic recording tape whose contact angle is 80° or more, as shown in Comparative Examples 2 to 9. 

What is claimed is:
 1. A magnetic recording medium comprising a non-magnetic substrate, an undercoat layer, a ferromagnetic metal layer, a protective layer and a lubricating layer formed in this order on the substrate, wherein the protective layer is a plasma-polymerized hydrogen-containing carbon film having, as formed, a refractive index of 1.90 or more, a film thickness of 30 to 150 Å and a contact angle with ion exchanged water of less than 80 degrees, the undercoat layer is a film formed of silicon oxide represented by SiOx (x=1.8-1.95), and the lubricating layer is formed of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds.
 2. A magnetic recording medium comprising a non-magnetic substrate, an undercoat layer, a ferromagnetic metal layer, an intercepting layer, a protective layer and a lubricating layer formed in this order on the substrate, wherein the protective layer is a plasma-polymerized hydrogen-containing carbon film (DLC film) having, as formed, a refractive index of 1.90 or more and a contact angle with ion exchanged water of less than 80 degrees, the undercoat layer and the intercepting layer are films formed of silicon oxide represented by SiOx (x=1.8-1.95), the total film thickness of the protective layer and the intercepting layer is 30 to 150 Å, and the lubricating layer is formed of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds.
 3. The magnetic recording medium according to claim 1 or 2, wherein the ferromagnetic metal layer is formed by vapor deposition.
 4. A method for producing a magnetic recording medium according to claim 1 which comprises forming an undercoat layer of silicon oxide represented by SiOx (x=1.8-1.95) on a non-magnetic substrate, forming a ferromagnetic metal layer thereon in a vapor phase, then plasma polymerizing a hydrocarbon gas and hydrogen at a frequency of 50 kHz to 450 kHz while applying a negative bias to a base side to form a protective layer of a hydrogen-containing carbon film having, as formed, a refractive index of 1.90 or more, a contact angle with ion exchanged water of less than 80 degrees and a film thickness of 30 to 150 Å, and finally forming a lubricating layer of a compound selected from the group consisting of polar perfluoropolyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds.
 5. A method for producing a magnetic recording medium according to claim 2 which comprises forming an undercoat layer of silicon oxide represented by SiOx (x=1.8-1.95) on a non-magnetic substrate, forming a ferromagnetic metal layer thereon in a vapor phase, forming an intercepting layer of a film formed of silicon oxide represented by SiOx (x=1.8-1.95) by plasma polymerization, then plasma polymerizing a hydrocarbon gas and hydrogen at a frequency of 50 kHz to 450 kHz while applying a negative bias to a base side to form a protective layer of a hydrogen-containing carbon film having, as formed, a refractive index of 1.90 or more and a contact angle with ion exchanged water of less than 80 degrees, adjusting the total film thickness of the protective layer and the intercepting layer to 30 to 150 Å, and finally forming a lubricating layer of a compound selected from the group consisting of polar perfluoro-polyethers, non-polar perfluoropolyethers, perfluorocarboxylic acids, phosphazens, perfluoroalkylates and perfluoroacrylate compounds.
 6. The method according to claim 4 or 5, wherein the negative bias is a pulse bias, the pulse duty factor (ON/OFF ratio) is 0.3 to 3, and the frequency is 10 Hz to 500 Hz.
 7. The method according to claim 4 or 5, wherein the formation of the ferromagnetic metal layer in the vapor phase is by vapor deposition. 